Setting the isolation level

Hello

I converted our application of transaction is not entitled to use transactions. I want to reduce the impact on performance, I setup some transactions to some lesser isolation levels. As I understand the documentation, the General method to do is to set the isolation level appropriate in TransactionConfig when you create a transaction.

But what I see in the documentation, it is possible to PrimaryIndex.get () third (lockMode) parameter allows you to specify isolation for the specific operation as well.

So my question is: what are the disadvantages of configuring isolation per-operation compared with the isolation by transaction configuration and accessories?

I.e. I'm considering the approach which is better:

1.
----
TransactionConfig txnConfig = new TransactionConfig();
txnConfig.setReadUncommitted (true);
Transaction txn = myEnv.beginTransaction (null, txnConfig);
for (id: idList)
{
primaryIndex.get (txn, id, null);
}
----

2.
----
Transaction txn = myEnv.beginTransaction (null, null);
for (id: idList)
{
primaryIndex.get (txn, id, LockMode.READ_UNCOMMITTED);
}
----

In general, I understand that specifying the isolation on a basic per-operation probably was to be used as a tool to locally modify the General transaction as a parameter

3.
----
TransactionConfig txnConfig = new TransactionConfig();
txnConfig.setReadUncommitted (true);
Transaction txn = myEnv.beginTransaction (null, txnConfig);
for (id: idList)
{
primaryIndex.get (txn, id, id == 5? LockMode.READ_COMMITTED: null);
}
----

but I want to know if the 2nd approach is legal and that it would not lead to some bad consequences.

Mikhail,

Blocking rules described in http://www.oracle.com/technology/documentation/berkeley-db/je/java/com/sleepycat/je/LockMode.html will help you to understand the interaction between operations and blocking rules. From there, you should see that specification of a lock at the level of the operation mode cancels and replaces all other levels of specifications.

In general, I understand that specifying the isolation on a basic per-operation probably was intended to be used as a > tool to change the setting of General transactions such as locally

Exactly, it's just an option of the API.

When you ask if (1) or (2) is better, both are equivalent, although it seems unusual that a transaction where you always choose to use READ_UNCOMMITTED. However, there are no differences in efficiency, and the choice must be made of the way in which it matches your code.

Kind regards

Linda

Tags: Database

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